The present invention relates to a threaded pedestal refrigerant cup, or threaded pedestal aerosol mounting cup, for use with a container carrying pressurized contents. The present invention also relates to a process for making such a threaded cup.
Pressurized liquids and gases, such as aerosols or refrigerants for example, are often stored and sold in small containers that are sealed with a mounting or refrigerant cup about the container neck. The conventional cup is formed from metal and has a substantially flat base with a peripheral rim having a skirt being integrally connected to the base by an outer wall. The cup further includes a cylindrical pedestal formed within a central area. During cup assembly, a plastic or rubber sealing material such as a gasket is placed within the peripheral rim of the cup between the outer wall and the skirt to sealingly engage the peripheral rim of the cup and the neck of the container. During the cup forming process, the pedestal is threaded such that a user may mount a corresponding threaded device on the pedestal to dispense the contents for an appropriate use. Once the cup is fully formed and assembled, the cup is positioned on the container. The container is then filled under the cup, or through a valve, or through the bottom of the container, by methods known in the art. The cup is sealed to the container by a crimping or clinching process known in the art.
A few different processes have historically been used to thread the pedestals of conventional cups. FIGS. 1 and 2 illustrate one method that has been used to thread a cup pedestal. FIG. 1 illustrates a sectional side view of a conventional steel pedestal 14a and a cylindrical arbor 26a having threads 28a. The arbor 26a is positioned to be inserted into the pedestal 14a. The pedestal 14a has a cavity 17a, an inner surface 18a, and an outer surface 22a. During the threading process, the pedestal 14a is threaded on both the inner surface 18a and the outer surface 22a simultaneously using offset matching threading devices. For example, the threaded arbor 26a is inserted into the pedestal cavity 17a and the threads 28a on the threaded arbor 26a machine the inner surface 18a as the outer surface 22a is simultaneously machined by any number of threading methods known in the art such as by a threaded arbor, rollers, wheels, threaded bars, etc.
FIG. 2 illustrates a sectional side view of an assembled cup 10a after the pedestal 14a has been threaded and a gasket 12a has been joined to the cup 10a. As shown, the threaded arbors operate to deform the pedestal 14a such that a rolled thread 30a with a nearly even thickness extends throughout the threaded area.
However, the process of FIGS. 1 and 2 suffers from a drawback. Using a threaded interior arbor 26a with another exterior threading tool to thread the pedestal 14a involves lengthy set-up time and some significant maintenance of the tooling. Also, perfect alignment of the interior arbor and the exterior threading tool must be maintained or the threads will be damaged.
FIGS. 3 and 4 illustrate another method that has been used to thread a cup pedestal. FIG. 3 illustrates a side sectional view of a conventional steel pedestal 14b with a non-threaded arbor 26b being positioned to be inserted into the pedestal 14b. During the threading process, the pedestal 14b is threaded on the outer surface 22b by inserting the non-threaded arbor 26b into the pedestal cavity 17b so that it engages the inner surface 18b while forming a thread on the outer surface 22b by an exterior threading tool known in the art.
FIG. 4 illustrates a side sectional view of the assembled cup 10b after the pedestal 14b has been threaded. As shown, the threading process produces a rolled thread 30b with a non-uniform thickness. This threading method leaves a smooth inner surface 18b of the pedestal 14b. Using the non-threaded arbor 26b results in lower tooling costs, easier set-up, and lower maintenance costs.
However, the process of FIGS. 3 and 4 suffers from drawbacks. For example, during the process, the metal is squeezed or extruded between the exterior threading tool and the non-threaded arbor 26b such that the metal has a non-uniform thickness along the threaded area. The thread 30b extends to an outer diameter 34 where the metal is thicker and to an inner diameter 38 where the metal is thinner. If a deeper thread is attempted, more stress and work hardening occurs during the threading process and the thread 30b can be weakened or broken. Work hardening is an increase in metal hardness that accompanies plastic deformation of the metal. Therefore, the speed of the thread rolling process is limited and the working life of the exterior threading tool is limited. Additionally, because the threading process results in non-uniform metal thickness over the threaded area, thicker raw material is necessary to accommodate certain thread depths.
Another threading process is disclosed in U.S. Pat. No. 4,515,285 issued to Euscher-Klingenhagen and shown in FIG. 5. The cup 10c is made from two thin layers of metal 42 and 46 sandwiched and then formed together as if they are one piece of metal. A non-threaded arbor is inserted into the pedestal 14c to engage the inner layer 46 while the outer layer 42 is threaded by an exterior threading tool known in the art. Only the outer layer 42 is threaded while the inner layer 46 remains generally intact. Because the inner layer 46 is not threaded, it does not break if the threaded outer layer 42 gets stripped or broken. This system of separate layers serves as a safety feature for containers carrying flammable contents because the inner layer 46 does not break even if the threaded outer layer 42 does.
However, the two metal layer process suffers from drawbacks as well. For example, the process is expensive, requires a separate gasket for use with the cup, and because the outer layer is so thin, the thread depth is extremely limited.
Therefore, a need exists for a thin threaded pedestal cup and a method for threading such a cup that overcomes the deficiencies of conventional cups and threading processes.